Virtually everyone relies on e-mail for personal and/or business communications. Thus, a plethora of e-mail servers, such as those made by Oracle® and IBM®, exist for local clients to handle transferring e-mails from one client to another. In addition, a variety of free e-mail servers exist over the Internet (e.g., Yahoo®, Google® Mail, and Hotmail®) that allow clients to send and receive e-mail through web browsers. In many instances, to send mail from one client to another, the e-mail must pass between different e-mail servers. For example, an e-mail originating on the Hotmail® server and addressed to a client on a Yahoo® server must pass from the Hotmail® server to the Yahoo® server.
In addition, many e-mail users today rely on hand-held wireless devices such as cellular telephones, Personal Digital Assistants (PDAs), and multipurpose devices which perform the functions of both cellular telephones and PDAs such as the T-Mobile Sidekick and Sidekick 2 designed by Danger, Inc., the assignee of the present application.
Certain wireless devices such as the Sidekick allow users to retrieve email messages from a variety of different e-mail accounts (e.g., Hotmail, Yahoo, etc). In the case of the Sidekick, for example, the data processing service over which the Sidekick operates is capable of retrieving and processing messages from these external e-mail accounts on behalf of the user.
Because of the proliferation of SPAM, viruses, and malware in today's technology, when an e-mail message is transferred from one service to another, the service may perform certain functions on the e-mail, such as filtering for SPAM and viruses. For some services, an e-mail may pass through multiple filters.
One problem which exists With this configuration is that, when multiple filters exist, all of the filters may not be necessary for a particular e-mail message. Another problem which exists with this configuration is that changes wrought by the filters may require a message to be re-filtered from the beginning. Given the large number of email messages processed by the data processing service, it is important to avoid redundant filtering since it may place a significant computational strain on the service.
To further exacerbate the problem, a process of removing unnecessary and/or redundant filtering must be secure so that senders of SPAM, unsolicited e-mails, and viruses are not able to exploit the process in order to circumvent filtering altogether (and thereby cause harm to a hand-held wireless device).